Purpose: :
Motivated by the success of cochlear implants for deaf patients,we are now facing the challenge of creating a visual prosthesis,based on a new generation of highly biocompatible and multifunctional3D intracortical microelectrodes designed to interface withthe occipital visual cortex as a means through which a limited,but useful visual sense could be restored in profoundly blindindividuals.

Methods: :
We developed in the framework of the European Project NeuroProbes,a new generation of multielectrode arrays (MEA) based on siliconshafts with a cross section of 100 x 120 microns. Basic 2D MEAswere integrated into 3D MEAs using a slim backbone and a modulartechnology. 4-shaft-combs with 36 electrodes made of smoothplatinum, electroplated platinum black or platinum/iridium wereimplanted in rabbit cerebral cortex. The electrodes were connectedto the recording/stimulating equipment using highly flexiblepolyimide cables. After several time periods the animals weresacrificed and the MEAs were explanted. The implanted site wasremoved and processed by immunohystochemical techniques.

Results: :
These probes are capable to penetrate into the brain at lowinsertion speeds without introducing excessive dimpling. Wesuccessfully recorded single and multi unit activity as wellas LPFs from cortical neurons. Neural recordings taken fromthe same electrodes before and after multiple electrical stimulationsessions were very similar in signal/noise ratio and in thenumber of recordable units. The continuous presence of the microelectrodesappears to result in a sustained response, at least partiallycomposed of reactive glia, that maintains a compact sheath whichisolates the microelectrodes from the brain.

Conclusions: :
The new NeuroProbes arrays are well tolerated by the centralnervous system. Our data suggest that this new generation ofMEAs can be used to record and stimulate cortical neurons andcould be used for a long-term stable and safe clinical neuroprosthesis.However more studies regarding possible damage of neural tissuesby permanent charge injection and the more effective means ofstimulating cortical tissue using this new generation of MEAsarrays are needed.